I've received a flood of emails since we launched the revamped Tekpub site (using Rails and MongoDb) a few months back. Many people have been surpised to find out that we use both MongoDb *and* MySQL. Here's the story of how we did it and why.
I’m a big fan of giving relational systems the boot when it comes to persisting application data. The more I work with document (or OO) databases, the more I feel really, really dumb for doing it any other way. One question that comes up a lot in conversation, however, is “dude what about reporting – you can’t do that with NoSQL very well now can ya?” and the answer is “yes, correct. You can’t”. As with all things programming: right tool for the right job.